1. Field of the Invention
The present invention relates to a zoom lens, which is suitable as an image pickup lens used in an image pickup apparatus.
2. Description of the Related Art
In order to fully utilize the potential of newly developed solid-state image pickup sensors, a compact zoom lens having a wide angle of view and a high zoom ratio over the entire zoom range is desired. Specifically, a zoom lens which is compact, has a wide angle of view, and offers a high zoom ratio would advantageously allow for the production of a small-sized and highly efficient photographic optical system used in an image pickup apparatus. In addition, a zoom lens having high optical performance over the entire zoom range can easily support new high-definition solid-state image pickup sensors.
A variety of zoom lenses are currently known. In particular, four-unit zoom lenses including first to fourth lens units having refractive powers of positive, negative, positive, and positive in order from an object side to an image side are widely known.
Among the four-unit zoom lenses, a rear-focus-type four-unit zoom lens is known. The four-unit rear-focus-type zoom lens is most generally configured to perform zooming by moving the second lens unit alone or by moving the second and third lens units. In addition, the four-unit rear-focus-type zoom lens can correct an image plane variation caused by the zooming by moving the fourth lens unit, and can perform focusing. U.S. Pat. No. 7,463,427, Japanese Unexamined Patent Application Publication No. 2002-244045 disclose four-unit rear-focus-type zoom lenses as described above.
In order to realize a wide angle of view, a high zoom ratio and a high optical performance over the entire zoom range, it is important to appropriately set the zoom type, the refractive powers of the respective lens units, the lens configurations of the respective lens units. In particular, in the case of the four-unit rear-focus-type zoom lens, it is important to appropriately set the positional relationship between the first lens unit and the second lens unit on an optical axis, the refractive powers of the first and third lens units, and the lens configuration of the first lens unit. Furthermore, appropriate setting of an amount of movement in association with zooming and imaging magnification of the second and third zoom lens units is important.